Engines may operate with various forms of combustion, one of which is Homogeneous Charge Compression Ignition (HCCI), where an air and fuel mixture achieves a temperature where autoignition occurs without requiring a spark from a sparking device. Combustion timing of HCCI engines may be controlled by regulation of the compression temperature of the charge, which in turn may be controlled by regulating the intake charge temperature (temperature of intake charge just prior to compression).
Various heat sources have been used to heat the charge as part of HCCI combustion control strategy, for example, heat generated from turbo charging the intake air, engine waste heat circulated by engine coolant, and/or waste heat harvested from the hot exhaust. However, the inventor herein has recognized that under certain circumstances, the above heat sources may be unavailable and/or unable to provide sufficient heat or sufficiently precise temperature control. For example, during engine cold start or idle, or when the engine is operated to charge the battery while the vehicle is parked, sufficient heat may be unavailable from the exhaust and/or the engine to heat intake air/charge. This may be especially true in hybrid vehicle configurations, where the reduced engine size and increased engine efficiency in HCCI-electric hybrid engines further decrease thermal energy availability for heating the intake charge.
While burners and heaters have been used to provide the additional heating needed for the intake charge (see, for example, U.S. Pat. No. 6,295,973 which describes an electrical heater installed at the intake air port for heating the intake air), such an approach may consume electricity and reduce fuel efficiency.
Applicants have thus recognized that the above issues may be addressed by harvesting various additional thermal energy sources to heat and control the temperature of the intake charge through one or more heat exchangers. For example, it may be possible to harvest heat generated by various components of an electrical power system of a HCCI-electric hybrid vehicle power train, such as inverter, rectifier, battery, and a regenerative braking system. Further, this approach may be especially suited to plug-in hybrid vehicles, for which the electrical power system may include an external plug-in.
As another example, excess electric power generated by a HCCI-electric hybrid vehicle that cannot be utilized for charging energy storage, or otherwise utilized, may also be used to heat the intake charge. In one embodiment, excess electric energy generated by the engine, and/or by regenerative braking system from regenerative braking when the battery is fully charged, or under high battery temperatures, and/or during excessive charging rates may be used to control temperature and heat the intake charge for HCCI combustion.
By providing a thermal management system for a HCCI-electric engine that harvests various sources of thermal energy and/or excessive or waste electric power, it may be possible to provide the additional heating and more accurate intake charge temperature control with reduced impact on fuel economy. In particular, by providing a thermal management system for a hybrid HCCI-electric engine that utilize various thermal energy and/or electrical power, it may be possible to operate the HCCI engine efficiently, even under conditions such as when the engine is used to charge the battery while the vehicle is parked.